Microbiomes of guppy populations translocated in Trinidadian streams

An organisms’ gut microbiome can alter its fitness, yet we do not know how
gut microbiomes change as their hosts evolve in the wild. We took
advantage of a five-decade ‘chronosequence’ of translocated fish
populations to examine associated changes in the gut microbiome.
Populations of Trinidadian guppies have displayed parallel phenotypic
convergence six times when moved from high predation (HP) to low predation
(LP) environments. Across four drainages, we found microbiomes of fish
translocated 5-6 years prior to sampling were already distinct from the
microbiomes of their HP source populations. Changes in environmental
conditions were most important in driving this shift, followed by
phenotypic shifts in gut morphology. After 30-60 years in LP environments,
microbiome composition was still distinct from native LP populations, but
microbiome function was not. We found some evidence that nitrogen fixation
enhanced gut nutrient absorption, but most functional shifts were not
parallel across drainages. Stream-and drainage-specific signatures were
present for both composition and function, despite our overall finding of
consistent microbiome change across drainages. As we unravel the
complexities of host-microbiome evolution in the wild, studies should
consider environmental microbial colonization, host phenotypic plasticity
in nature, and more realistic environmental conditions excluded from
laboratory studies.